Many known combustion turbine engines burn a hydrocarbon-air mixture in a combustor assembly and generate a combustion gas stream that is channeled to a turbine assembly. The turbine assembly converts the energy of the combustion gas stream to torque that may be used to power a machine, for example, an electric generator or a pump. The combustion gas stream temperature prior to the first stage nozzle is referred to as the combustor exit temperature. A common range of combustion gas stream temperatures may be approximately 2400° F. to 2600° F.
Typically, when a turbine is operated at a relatively high load, the combustor exit temperature is high and carbon monoxide (CO) and/or unburned hydrocarbon (UHC) emissions are held to a minimum. However, when the combustion process is not fully completed, high levels of CO and/or UHC may exist in the turbine exhaust system. High CO and/or UHC emission levels are prohibited by regulatory agencies.
In typical combustion turbine engines, the ability of the hydrocarbon fuel to completely combust is limited by a lower limit on the combustor exit temperature. As the turbine load decreases (often referred to as “turn down”), it is necessary, in many gas turbines, to reduce the combustor exit temperature, and the lower temperature limit can be violated, which may result in increased levels of CO and UHC being formed. What is needed is a way to maintain high combustor temperatures to prevent an increase in CO and/or UHC emissions to unacceptable levels when a turbine engine reduces load.